Polishing apparatus

ABSTRACT

In a polishing apparatus having a cover body with fluid pressing mechanism, during polishing, vibration and migration of sticking portion between a retainer and a membrane generated in downstream of rotation of a polishing platen is prevented by reducing sticking force between the retainer and the membrane to less than force needed to wafer polishing with rotation of the cover body.

FIELD OF THE INVENTION

The present invention relates to a polishing apparatus, which, inparticular, is suitable for planarization of surfaces of work piecessuch as semiconductor wafers for semiconductor integrated circuitdevices with a multilayer interconnection comprising a plurality ofmetal films.

BACKGROUND OF THE INVENTION

Recently, it is seen that planarization of surfaces of interconnectsubstrates for large scale semiconductor integrated circuits (referredto as “LSI”s hereafter) is important. One of representative techniquesfor the planalization is the Chemical Mechanical Polishing; CMP(referred to as “polishing” as long as there is not any notification).

The polishing techniques are classified roughly into two processes:

a process utilizing a mechanical polishing property of abrasive grains;and

a process dominantly utilizing a chemical surface reaction effect withpolishing with abrasive grains enhancing the reaction.

The former process is mainly used for planarization of insulator filmssuch as silicon oxide (SiO₂), alumina (Al₂O₃), or silicon nitride (SiN).An example, in which polishing of SiO₂ is applied to semiconductorintegrated circuit fabrication, is described, for example, “PROCEEDINGSVLSI MULTILEVEL INTERCONNECT CONFERENCE 1991, A POUR-LEVEL-METAL FULLYPLANARIZED INTERCONNECT TECHNOLOGY FOR DENSE HIGH PERFORMANCE LOGIC ANDSRAM APPLICATIONS” 20-26. Concentration of abrasive grain in slurriesfor these polishing process is generally high, often ranging in 10-25weight percent.

The latter process, in which chemical reaction mainly works, is mainlyused for metal-film planarization, and described in detail, for example,in JP-A-2-278822 specification and JP-A-8-83780. Concentration ofabrasive grain in the slurries is often 5 weight percent or less. Aprocess, in which metal-films are polished in a liquid containingsubstantially no abrasive grain, is disclosed JP-A-11-195628.

It is assumed that an in-between process of the above two processes ispolishing of (Si) substrate. Slurry for insulator is used in thesubstrate polishing, but it is thought that dominance of chemicalreaction effect with respect to mechanical polishing effect in thesubstrate polishing process is greater than the one in SiO₂ polishingprocess.

Additionally, processes to polish silicon wafers, glass substrates, orthe like, in which instead of polymer-resin polishing pad, a polishingpad with fixed abrasive grains such as silica or cerium oxide (referredto as “grindstone” hereafter) is used and slurry itself does not containany abrasive grain, are disclosed in such as JP-A-10-125880 orJP-A-8-64562. A process to polish copper using similar grindstone isdescribed in “PROCEEDINGS SEMI TECHNOLOGY SYMPOSIUM 1998, A NEWSLURRY-FREE CMP TECHNIQUE FOR CU INTERCONNECTS” 5-72 to 5-78. Howeverconsideration must be made, since principle of each of above methodsusing such fixed abrasive grains is similar to principle of polishingusing slurry with respective abrasive grain and therefor the methodeasily generate polishing damage while having good planarizing effect.

It is necessary that polishing is performed uniformly over apredetermined area of an interconnect wafer when above mentionedpolishing process is applied for planarization of surface of theinterconnect wafer. In order that polishing is performed uniformly, itis needed that at least a surface of an interconnect wafer, which is tobe polished, is pressed onto a polishing pad with uniform pressure. Foruniform pressing, a variety of polishing apparatuses, particularlycarrier structures to hold an interconnect substrate therein andmechanism for applying uniform pressure onto an interconnect substratein the carriers, are being developed.

Fluid pressing mechanism is known as a carrier structure suitable foruniform pressing. As the fluid pressing mechanism, two type is known; atype of mechanism in which pressure is applied with air or liquid ontobackside of an interconnect wafer (referred to as “direct fluid pressingmechanism” hereafter), and a type of mechanism in which pressure isapplied by pressing a flexible rubber-like sealed bag onto backside ofan interconnect substrate (referred to as “fluid bag mechanism”).

The latter, as an example described in “The Japan Society for PrecisionEngineering, Autumn Conference 1991, conference paper publication, TRIALMANUFACTURE AND BASIC CHARACTERISTICS OF POLISHING APPARATUS” 211-212,has a structure wherein pressure applied onto a carrier is transmittedthrough a fluid bag constituted by a balloon-like membrane to aninterconnect substrate and wherein an annular retainer surrounds aninterconnect substrate to confine the substrate during polishing.Pressing onto an interconnect substrate is carried out by filling gaswithin the fluid bag. It is assumed that pressing with such fluid bagprovides uniform pressing over backside of an interconnect substrate. Inthis example, the fluid bag is not secured to periphery of a substrate.Sealed container filled with fluid is pressurized by a weight. Since theweight or the fluid bag is not fixed, a guide is further providedoutside of the retainer in order to prevent them coming off.

As described above, polishing apparatuses in which a weight or a fluidbag is not secured to a guide, are not suitable for polishing of manyinterconnect substrates since load and unload of an interconnectsubstrate are complicated. To solve the problem, a mechanism wherein afluid bag is secured to a carrier is used recently.

The portion of a carrier that contacts with an interconnect substrate isprovided with substantially planar surface, since once foreign materialsinfiltrate into the mechanism when polishing is performed they maygenerate polishing damage or contamination. For example, surface andinner surface of the retainer are finished with surface smoothness suchthat they have luster. A membrane composing the fluid bag is flexibleand made of flexible rubber material with large friction such asneoprene or soft silicone. Therefor the membrane does not have lusterlike the retainer, but is finished with generally smooth surface. In thedirect fluid pressing mechanism, rubber-like or polymer-resin-like layerwith smooth surface is made contact only with periphery of backside ofan interconnect substrate, and pressing is then carried out byincreasing fluid pressure on the backside of the interconnect substratewhile retaining them in sealed states or the similar states.

In all cases above mentioned for fluid pressing mechanism, torque forrotating an interconnect substrate is first applied to the carrier, thenapplied to the interconnect substrate through elastic material or thinfilm of rubber-like material or polymer resin. The interconnectsubstrate is thus supported flexibly, and a characteristic is providedthat a substrate is secured to carrier or other transfer mechanism whileallowing twist and eccentricity. Such mechanism in a polishing apparatuswith fluid pressing mechanism consists of membrane composing flexibleportion contacting with an interconnect substrate and a flexor thatconnects a carrier with the membrane.

As described above, for use in polishing of interconnect substrates forsuch as semiconductor integrated circuit devices, a variety of slurriesthat have not only mechanical effect but also surface chemical reactioneffect, and polishing apparatuses comprising a carrier with fluidpressing mechanism such as fluid bags, have been developed.

However, a problem for unstable polishing arise in that polishing byusing such polishing apparatus with fluid pressing mechanism andchemical-effect-dominant slurry often results in periodical highfrequency sound (high frequency noise) generation and significantlylowered polishing rate. Such unstable polishing usually does not occurwhen slurry for insulator is used, but frequently occurs when slurryutilizing surface chemical reaction and having abrasive grain atconcentration of 5 weight percent or less, i.e. slurry for metalcontaining substantially no abrasive grain, is used. When slurrysubstantially no abrasive grain is used, unstable polishing does notoccur if a conventional polishing apparatus with pressing mechanismother than fluid pressing mechanism.

As described above, there is a problem that it is difficult to utilizein stable manner the combination of chemical-reaction-dominant slurrycontaining low or substantially no abrasive grain and causing littlesurface damage of interconnect substrates, and a polishing apparatuswith fluid pressing mechanism providing good uniformity.

SUMMARY OF THE INVENTION

The present invention provides a polishing apparatus suitable forworkpieces such as semiconductor wafers for semiconductor integratedcircuit devices.

The present invention further provides a polishing apparatus forimproving polishing performance and for reducing high frequency noisegeneration when polishing a workpiece such as semiconductor wafers insemiconductor integrated circuit devices manufacturing.

The present invention further provides a polishing apparatus forsemiconductor integrated circuit devices for polishing a surface ofmetal film into stable and planarized state using slurry, or polishingsolution (or polishing agent) containing substantially no abrasivegrain.

The inventor first assumed that sliding occurs between a workpiece(referred to as “wafer” hereafter) and a membrane, causing wafervibration during polishing. Based on the assumption, porous resin layerwas inserted between the membrane and a wafer to increase the frictionbetween them, but substantial improvement was not made. Additionally,based on an assumption that the too flexible membrane causes pressingunstable, membrane hardness was increased, but any substantial effectwas obtained.

Regarding causes of such unstable polishing, the inventors noticed thefact that polishing is stably performed with mechanical-effect-dominantslurry containing high concentration of abrasive grain even if the fluidpressing mechanism is used. Therefore, to slurry containingsubstantially no abrasive grain, described in JP-A-11-195628, aluminapowder was added as abrasive grain such that the mixture hadconcentration of 10 weight percent of alumina. The polishing was thenapplied copper film on a wafer surface using the 10 percent mixture. Itwas then confirmed that above mentioned unstable polishing did notoccur.

The present invention is directed to slurry with concentration ofabrasive grain of 5 percent or less, and polishing solution (orpolishing agent) to which no abrasive grain is intentionally added.There are many differences in composition and feature between above twosubstances, but both have same behavior regarding the object of thepresent invention. In this sense, both will be referred to as “slurrycontaining substantially no abrasive grain”, hereafter.

Based on those characteristics, the inventor found that high frequencynoise is generated through mechanism described below, and came up with ameasure to reduce the noise from a viewpoint of the mechanism, thenverified that the measure is effective.

When slurry with high concentration of slurry in a polishing apparatuswith fluid pressing mechanism is used, a fluid bag first (hence amembrane,) expands for pressing. Since a polishing pad is movingrelatively with respect to the wafer (,hence providing relative motion,)during polishing, a membrane side of the fluid bag in the carriercontacts with inner wall of the retainer at the most downstream portionof the relative motion. Because the fluid bag has certain degree offreedom with respect to rotation of entire carrier, and friction betweenthe wafer and a surface of the polishing pad on a polishing platen islarge, the fluid bag does not necessarily follow the rotation of thecarrier or retainer completely, and it may cause twist of the membraneor flexor, or eccentricity of the membrane. However, since abrasivegrains infiltrated between membrane and retainer are sandwiched betweenthe membrane side and the retainer, the contacting between them ismaintained stably, and the fluid bag continues to rotate with the twistwith certain delay with respect to the carrier.

As a contrast, when slurry containing abrasive grain in lowconcentration of 5 weight percent or less, or substantially no abrasivegrain is used, the effect of abrasive grain is not sufficient so thatside of the membrane contacts with inner wall of the retainer at themost downstream potion of the relative motion on start of polishing.When slurry contains abrasive grain as well surfactant, even though itcontains abrasive grain, the side of membrane sticks tightly with theretainer, causing the membrane and a wafer to rotate following rotationof the carrier and retainer.

The force needed to break the sticking state (referred to as “stickingforce” hereafter) is a power generated by the relative motion between awafer and the polishing pad. In other hand, a predetermined force isneeded to rotate a wafer through carrier, and is referred to as“rotational friction”. In the case of slurry with low concentration ofabrasive grain, rotational friction is less than sticking force.However, as the carrier rotation is continued, thus the sticking portionmoves laterally or upstream from the most downstream, sticking forcebetween the retainer and membrane is reduced, and the sticking state isbroken at the moment when sticking force become less than rotationalfriction, then new sticking portion is generated at the most downstreamportion of the relative motion.

In repeating such separation of sticking portion or generation of newsticking portion, high frequency noise is generated due to friction orvibration between side of the membrane and a inner wall of the retainer.Such vibration lowers sticking firmness between a wafer and thepolishing pad, reducing polishing rate. The inventers found those facts.

The inventers also found that in order to prevent such generation andbreakup of sticking potion, and generation of new sticking portion,methods described below is effective.

In the specification, since a carrier comprising a case (box body) towhich an elastic membrane secured, and retainer (wafer receptor)attached to bottom of the case covers side and a backside of a waferplaced on a polishing platen, the carrier is referred to as “coverbody”. Additionally, the carrier is referred to as “wafer holder”, sincethe carrier hold a wafer over the polishing platen during polishing withfluid pressure within the carrier.

The inventor found that stable polishing is provided without highfrequency noise generation by using polishing apparatus employing one orcombination of following three methods. The first method is such thatsticking force between the membrane and the retainer (a receptor of aworkpiece like a wafer) is reduced to less than rotational friction. Thesecond method is such that the retainer is made rotatable with respectto the case (box body) of the carrier (cover body or holder for a wafer)so that sticking portion between the retainer and the membrane does notmove. The third method is such that flexor strength is increased so thatthe membrane does not easily stick to the retainer.

Specifically, in the first method, by composing inner wall of theretainer, which contacts at least with the membrane, of material toreduce the sticking force between the membrane and the retainer to lessthan the rotational friction, it is ensured that sticking portion isalways at the most downstream portion. Fluorocarbon resins such astetrafluoroethylene or trifluoroethylene, are suitable for suchmaterial.

Another method to lower the sticking force is to provide grooves orheight variation in surface of the inner wall of the retainer such thatthe retainer does not easily sticks to the membrane. It is confirmedthat depth and pitch of the groove or height variation is preferablylarger than size of abrasive grain size of used slurry, and size largerthan 10 micron provides practical and stable lowerd sticking force. Byprovision of plurality of such grooves in longitudinal or lateraldirection, abrasive grain or slurry is actively retained in the groves.

A still further method is to lower sticking force by coating fluororesinin thickness of 10 micron to 100 micron onto side of membrane opposingto inner wall of the retainer, or by providing side of the membrane withgrooves or height variation. Combination of them can further reducesticking force and is thus effective in prevention of unstablepolishing.

In any of above methods, pressure of fluid is controlled, the fluid isintroduced to expand the membrane such that a wafer rotates while theside of the membrane is pressed onto the inner wall of the retainer tocontact therewith.

In the second method, a retainer has a structure to be rotatable withrespect to the case of the carrier so that the retainer and membranealways can rotate together and sticking portion therebetween is retainedstably at the most downstream of the relative motion without undesiredfriction. The method is in principle most suitable for prevention ofunstable polishing. However, it preferably use a structure such that itcan decrease possibility that abrasive grains or foreign particleinfiltrate into the mechanism which allows the retainer rotate withrespect to the carrier case, generating new particles, then generatingpolishing damage.

In the third method, strength of a flexor, which is an elastic fixingmember for the membrane, is increased so that sticking between amembrane and a retainer, or migration of sticking potion does not easilyoccur that would otherwise occur due to twist. As a flexor, thin film ofrubber or polymer resin in thickness of 0.5 mm or less may be used,however it is preferable that the thickness is more than 0.5 mm and thatthe effective strength is increased more than two times by using hardermaterial. Thin plate made of stainless steel or phosphor bronze that hasgood elasticity, or hard resin with high wear resistance such aspolyurethane resin, fluorine-contained resin, silicone resin, or nylonresin, is suitable for the hard material. Since this method allowsmembrane to move upward and downward with respect to the retainer, themembrane does not easily twist with respect to the entire carrier, andnot easily stick to the retainer due to deformation. However, a cautionshould be made that too high flexor strength lowers polishinguniformity.

By using one of above described methods, or any combination of them,generation of high frequency noise and unstable polishing can beprevented. Particularly, it is significantly effective in polishing ofmetal film with slurry containing substantially no abrasive grain.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross section view of main portion of a polishing apparatus;

FIG. 2 is a detailed cross section view of main potion of a polishingapparatus;

FIG. 3 is a detailed cross section view of main potion of anotherpolishing apparatus;

FIG. 4 is a partial perspective view of a retainer in a polishingapparatus;

FIG. 5 is a partial perspective view of a retainer regarding an exampleof the present invention;

FIG. 6 is a partial perspective view of a retainer regarding anotherexample of the present invention;

FIG. 7 is a partial perspective view of a retainer regarding anotherexample of the present invention;

FIG. 8 is a partial perspective view of a retainer regarding stillanother example of the present invention;

FIG. 9 is cross section view of main portion of polishing apparatusregarding another example of the present invention;

FIG. 10 is cross section view of main portion of polishing apparatusregarding still another example of the present invention;

FIG. 11 is a cross section view to describe a manufacturing process ofsemiconductor integrated circuit device;

FIG. 12 is a cross section view to describe a manufacturing process ofsemiconductor integrated circuit device;

FIG. 13 is a cross section view to describe a manufacturing process ofsemiconductor integrated circuit device; and

FIG. 14 is a cross section view to describe a manufacturing process ofsemiconductor integrated circuit device.

DETAILED DESCRIPTION OF THE INVENTION EXAMPLE 1

FIG. 1 shows a cross section of main portion of a polishing apparatusused in the present invention. A polishing pad 11 is adhered onto mainsurface of a rotational polishing platen 10, and slurry (not shown)containing substantially no abrasive grain, is supplied by a supplyinlet 13. Size of the polishing pad 10 is eighteen inch in diameter inexamples described below as long as there is not any notification. Awafer 100 consisting of four-inch-diameter silicon wafer, on surface ofwhich one-micron-thickness Cu film (not shown) is formed, is pressedonto the polishing pad 11, with the wafer covered with a cover bodycovering the wafer or by a holder body (a carrier) 12 holding the wafer.A dresser 14 to process surface of the polishing pad (so-called“dressing”), is mounted on another main portion of the polishing platen10, and textures the surface of the polishing pad by rotating it withpressing.

A foamed polyurethane resin pad, IC1000 (trade mark of RODEL) was usedfor the polishing pad 11. Ring shape dresser PCR-103 (trade mark ofNANOFACTOR) was used for the dresser 14. As polishing solution for Cu,solution as described in JP-A-11-195628 was used, which contains malicacid as solvent for oxide layer, BTA as protection layer formationagent, and hydrogen peroxide as oxidizer. No abrasive grain is containedin the polishing solution. The polishing solution was supplied at flowrate of 50 milliliter per minute. To this slurry containingsubstantially no abrasive grain, surfactant for stabilization was added.

First, the wafer 100 was polished with polishing pressure thereon of 200g/cm² while dressing was performed by the dresser 14 that was pressedwith pressure of 110 gf/cm². Rotation speed of the polishing platen 10was 90 rpm.

FIG. 2 and FIG. 3 is detailed view of the structure of a cover body orcarrier 12A that the inventor used. A case 101 in upper potion of thecarrier 12A had inner space and open bottom portion. Onto lower side ofthe bottom potion, a workpiece receptor (or a retainer) 102 is attachedin order to confine the wafer 100. The retainer 102 is made of resinwith high wear resistance, for example, such as polyurethane, epoxide,nylon, polypropylene, or polyphenylsulfide.

In the case 101, a fexor member (flexor) 104 is provided, and inner edgeof the flexor contacts closely with a support plate 105 to support amembrane. The support plate 105 has one or more openings for passingair, liquid, or the like therethrough, as described below.

A membrane 103 made of elastic material such as neoprene rubber with 0.5mm thickness is also the support plate 105, lower side of the membranecontacts with backside of the wafer 100, and side of the membrane isopposing to retainer 102.

In the present invention, material that has elasticity such that itexpands or restores the initial state depending on pressure of air orliquid described below, is suitable for the membrane 103. It preferablyhas resistant against at least fluid pressure of 500 gf/cm² as maximum.

The elastic membrane 103 is thus secured to the case 101, hence innerwall of a carrier 12A. The inner space of the case is made as sealedstructure (referred to as “fluid bag structure”) that is sealed fromouter region, by using the case 101, the flexor 104, and the membrane103 in combination. Fluid is introduced (injected) by introducing hole(injection inlet) 106 for fluid such as air or liquid, and the elasticmembrane is expanded to contact closely with the backside of the wafer100, and predetermined pressure is applied onto the backside of thewafer 100 in the direction toward the polishing platen 10 or thepolishing pad 11. Such state is kept during polishing operation. Sincethe flexor 104 and the membrane 103 is made of flexible material andthus can be transformed, the wafer 100 may move up or down, beeccentric, and twist to certain extent with respect to the retainer 102.

FIG. 3 shows a structure in which openings are formed at least in a partof membrane 103A so that the wafer 100 is pressed directly by fluid.Thus, inner space of the carrier 12A inner is sealed by wall of the case101, the flexor 104, the membrane 103A and the wafer 100 seal.

There is almost no difference in pressing mechanism for the waferbackside between FIG. 2 and FIG. 3. For simplification of explanation, acase of polishing apparatus with the fluid bag structure in FIG. 2 willbe described hereafter. The occurring phenomena and provided effects aresubstantially the same in both cases.

For such a carrier 12A, a ring-shaped retainer 202 of epoxide resin,inner wall of which is smoothed in certain extent, is used as shown FIG.4.

On the other hand, an example of the present invention is characterizedthat a retainer as shown in FIG. 5 is used. Body of a retainer 202A ismade of epoxide resin, into at least potion of inner surface (or innerwall) in the retainer that may contact with membrane 103, a ring 202B oftetrafluoroethylene resin is embedded. Fluorocarbon resin such astrifluoroethylene resin or fluorovinylidene resin may be used instead oftetrafluoroethylene. The ring 202B has an effect that friction withmembrane 103 is significantly reduced comparing to epoxide resin that istypically used.

Such a carrier in FIG. 5 was utilized in the polishing apparatus in FIG.2, then polishing was performed over a sample wafer. The sample waferwas such that 50 nm tantalum then 800 nm copper had been stacked on awafer in which oxides had been formed on its surface. As a result,stable polishing was provided during copper polishing, and highfrequency noise was not generated. Polishing rate was 250 nm/min.However, at time when copper film polishing was completed and tantalumfilm was exposing, high frequency noise was generated. However, sincethe slurry is not intended for tantalum film polishing, there is not anyproblem in practice. In comparing tetrafluoroethylene resin with anotherresin, such as trifluoroethylene for example, tetrafluoroethylene resinis best in that its friction is lower. However, regarding wearresistance, it is not suitable, and a number of other fluororesins suchas trifluoroethylene are better.

On the other hand, polishing was performed in same condition, by usingthe carrier mounted with a retainer of epoxide resin, inner surface ofwhich had been smoothed. Since starting of polishing, large, highfrequency noise was generated. Polishing rate of copper film was reducedto less than 50 nm/min, and much polishing damage occurred on surface,and polishing was not stable.

EXAMPLE 2

Polishing was performed in same condition as the example 1, except thata retainer shown in FIG. 6 or FIG. 7 was used.

Specifically, a retainer 202C of FIG. 6 is made from typical epoxideresin. In the retainer 202C, a plurality of grooves 203 with V-shapecross section of 10-500 micron depth are formed at least into inner wallthat may contact with the membrane 103, substantially in parallel withsurface (retainer polishing surface) of the retainer where retainercontacts with the polishing pad (hence laterally). It was founded thatthe depth variation of 10 to 500 micron was generated as follows. Aretainer of resin is usually not accurate circle, and necessarily has acertain deformation. The retainer in this example was also deformed,thus depth of the deepest groove was 500 micron, and depth of theshallowest groove was 10 micron. Groove angle of the V-shaped groove 203was about 90 degrees. The groove formation decreased surface area thatcan contacts with the membrane 103 (referred to as “effective surfacearea”) to half of the initial one. Additionally, even if the membrane ispressed onto the retainer with said pressure, there is always slurry atbottom of the V-shape groove 203, sticking force between the membrane103 and the retainer 202C can be thus substantially reduced.

In the case of an retainer 202D in FIG. 7, a plurality of V-shapegrooves 204 of 10-100 micron depth is formed at least into inner wall ofa part that may contact with membrane 103, in direction crossing withmain surface of the polishing surface or polishing platen (hencelongitudinally).

An carrier comprising such retainer structure 202C or 202D as shown FIG.6 or FIG. 7 was employed in the polishing apparatus in FIG. 2, a sampleconsists of similar wafer as the example 1 (an interconnect substrate)was then polished. As a result, stable polishing was provided duringcopper polishing, and high frequency noise was not generated. Polishingrate was 250 nm/min. However, at time when copper film polishing wascompleted and tantalum film was exposing, high frequency noise wasgenerated. However, the slurry is not intended for tantalum filmpolishing as described above, therefore there is not any problem inpractice. In comparing the parallel lateral groove and the crossinglongitudinal groove, the former has an advantage that it is easilymachined, and the latter has a disadvantage that abrasive grain ofslurry easily remain within the grooves while having an advantage thatit is easy to inject or drain slurry and an advantage that retainercleaning is easy.

EXAMPLE 3

A wafer was polished in same condition as the example 1, except that aretainer in FIG. 8 was used. The retainer 202A, 202C is made of materialof typical epoxide resin. In the retainer, ring 202 a made oftetrafluoro resin with low coefficient of friction is embedded intoinner wall of a part that may contact with the membrane, and a pluralityof grooves 203A with V-shaped cross section and about 100 micron depthis formed substantially in parallel with the polishing surface, hencelaterally. Groove angle of the V-shaped groove 203A was about 90degrees. Use of resin with low coefficient of friction as well asformation of the grooves allowed surface area that may contact with themembrane to decrease to half of the initial one.

A carrier with a retainer as shown in FIG. 8 is employed in a polishingapparatus, then a sample of wafer similar to one in the example 1 (aninterconnect substrate) was polished. As a result, stable polishing wasprovided during copper polishing, and high frequency noise was notgenerated. Polishing rate was about 250 nm/min. Additionally, highfrequency noise was not generated too when copper film polishing wascompleted and tantalum film was exposed.

Preferable conditions for the grooves as described in the example 2 or3. If cross section shape of grooves is V-shape, it is easy to machineit. But cross section shape is not limited to the V-shape. If depth ofV-shaped grooves is at least more than 1 micron, it is effective. Thisis because size of abrasive grain in slurry is often 50 nm or less, andthe depth is preferably more than the size. In terms of themachinability, the depth of the V-shaped groove is preferably equal toor more than 10 micron. When only depth of the grooves is increased butthe width is not increased so that effective surface area is reduced,the groove cross section may be inverted trapezoid. Reduction of grooveangle of the groove or the side allows formation of more grooves.However, a problem occurs that foreign materials easily stick to them,resulting in difficulty in cleaning of the grooves. As the groove angle,60 degree or more, preferably 90 degree or more is suitable. Themachined surface may be also curved by making the grooves' cross sectionin partial arc or partial elliptic arc, or in their combination,although machining is difficult. The groove shape makes cleaning mucheasier. Longer life may be also provided due to lower membrane damage.

As an alternative method for the groove formation described above, it iseffective to texture inner side (inner wall,) of the retainer. Heightdifference in the height variation of 1 micron or more is effective,however, height difference of 5 micron or more is preferable to makeprocessing easier. The surface-texturing is simple process, for whichsand blast process may be utilized, and has a problem that it isdifficult to control repeatability of surface textured state. Theproblem that foreign material is easily built up may occur depending onthe condition of the surface-texturing.

EXAMPLE 4

FIG. 9 is used for description. It is characterized in thatconfiguration of retainer and case is different from above examples. InFIG. 9, a retainer 302A to confine a wafer (an interconnect substrate)300A during polishing is rotatably mounted in lower portion (bottomportion) of a case (box body) 301 in an carrier 12B. For the retainer302A, epoxide resin is used as a high wear resistive resin. To innerwall of the case 301, a flexor 304 made of neoprene rubber or the likeis secured, and inner edge of the flexor is made contact closely with asupport plate 305. To the support plate 305, a membrane 303 made ofneoprene rubber or the like is secured, and lower surface of themembrane contacts with backside of the wafer (an interconnect substrate)300, and side surface of the membrane opposing closely to the retainer302A. Fluid is injected through a fluid injecting inlet (introducinghole) 306 in upper potion of the carrier 12B, pressing the wafer (theinterconnect wafer) 300 with predetermined pressure.

In this example, the retainer 302A is mounted in bottom portion of thecase 301 through a rotational mechanism 302B, and can thus rotate withrespect to the case 301. The rotational mechanism 302B may be a bearing,or a sliding mechanism with low resistance made of low-frictionmaterial. In this example, the rotational mechanism 302B was madeslidable by inserting a sheet of tetrafluoroethylene resin between thecase 301 and the retainer 302A.

By using a polishing apparatus with such carrier, a sample of wafersimilar to the one in the example 1 (an interconnect substrate) waspolished. As a result, stable polishing was provided, and high frequencynoise was not generated during copper polishing. Polishing rate was 250nm/min. Additionally, high frequency noise was not generated too whencopper film polishing was completed and tantalum film was exposed. Thisretainer structure was most suitable for prevention of unstablepolishing, although it has a problem that the entire retainer structurewas complicated. It is because unstable polishing discussed in thepresent invention should not be generated in principle. It also providesbetter cleaning performance since it is not needed to provide groove ininner surface of the retainer (surface of inner wall).

EXAMPLE 5

FIG. 10 is used for description. In the figure, a carrier of thisexample is pressed onto the polishing pad 11, and polishing isperformed. To lower surface (bottom portion) of a case (a box body) 401of a carrier 12C, a retainer 402 to confine a wafer (a interconnectwafer) 400 during polishing, is mounted. The retainer 402 is made oftrifluoroethylene resin. A flexor 404 made of thin plate of stainlesssteel with 0.1 mm thickness is secured to inner side (inner wall) of thecase 401, and inner edge of the flexor is made closely contact with asupport plate 405. To the support plate 405, a membrane 403 of neoprenerubber is also attached, and lower surface of the membrane 403 contactswith the wafer (an interconnect substrate) 400, and side surface of themembrane is opposing to the retainer 402. Predetermined pressure can beapplied onto backside of the wafer (an interconnect substrate) 400 byinjecting fluid through a fluid introducing hole (a injection inlet)406.

Possibility that the membrane 403 contacts with the retainer 402, can bereduced extremely, or eliminated, since due to increased hardness of theflexor 404, the membrane 403 and the wafer (an interconnect substrate)400 can move upward and downward in a certain extent with respect to theretainer 402 while eccentricity or deformation like twist does noteasily occur.

Polishing similar to the example 1 is performed by using a polishingapparatus with such carrier. As a result, stable polishing was provided,and high frequency noise was not generated during copper polishing.Polishing rate was 250 nm/min. High frequency noise was not generatedtoo after copper film polishing was completed and tantalum film wasexposed. However, for this carrier structure, a caution should be madethat the flexor 404 of stainless steel is expensive, and corrosion mayoccur depending on chemical composition of slurry.

EXAMPLE 6

An example in which a polishing apparatus according to the presentinvention is used in manufacturing of a semiconductor integrated circuitdevice, will be described with reference to FIG. 11 to FIG. 14 whichshow respective cross section of main portion for each process step. Thepolishing apparatus in this example had a structure wherein it compriseda carrier with a retainer of FIG. 8 as described in Example 6 of thepresent invention, and two polishing platens. Copper polishing isperformed on a first polishing platen with slurry containingsubstantially no abrasive grain as the example 1, Polishing overtantalum-based barrier film is performed on a second platen. And, theinsulator film and tangsten film are polished with another manufacturingmachine (not shown). In this example, insulated-gate transistors areformed as semiconductor device. In the case of dynamic random accessmemory or the like, the process to form electrode plates for elementsand the process after it, is substantially same as this example, whilesteps to form capacitors are added.

Polishing conditions for copper polishing were like following. Rotationspeed of 18 inch diameter polishing platen was 100 rpm, polishingpressure was 200 gf/cm², flow rate of slurry containing substantially noabrasive grain was 0.1 litter/min, the polishing pad was IC1000 made ofpolyurethane foam resin, temperature during polishing was 28 Celsiusdegree.

As shown in FIG. 11, embedded insulator layer 511 for isolating devicesfrom each other was formed into surface of an interconnect substrate 510comprised of 6 inch diameter silicon wafer containing p-type impurity.Its surface was planarized by polishing with alkali slurry containingsilica abrasive grain and ammonia. Diffusion layers 512 (semiconductorregion) containing n-type impurity were then formed by ion implantation,heat process, or the like, and gate insulator films 513 were then formedby thermal oxidation or the like. Gate electrodes 514 consisting ofpolycrystalline silicon, or stacked layer of refractory metal andpolycrystalline silicon were then formed through processing. Ontosurface of them, device protection film 515 made of silicon oxide,phosphorous doped silicon oxide or the like, and contaminationprevention films 516 made of silicon nitride or the like, to preventcontaminant penetration from outside, were deposited. Planarized layer517 made of silicon oxide (p-TEOS) formed by plasma chemical vapordeposition (plasma-CVD) using tetraethoxysilane (TEOS) as sourcematerial was formed in 1.5 micron thickness, and is removed by 0.8micron by using typical insulator polishing technique, so as to beplanarized. The surface of them was further coated with a secondprotection layers 518 of silicon nitride for preventing copperdiffusion. Contact holes 519 for connection with device were then formedin predetermined portion, and stacked layer 520 of titanium, andtitanium nitride layers for both adhesion and contamination preventionwas then formed, and tungsten layer 521 was then formed into the holes.Polishing was applied over portion except hole region to form so-calledplug structure.

The stacked layer 520 of titanium and titanium nitride is formed byreactive sputtering or plasma-CVD. Tungsten may be also formed bysputtering or CVD. At that time, size of contact holes 519 weregenerally 0.25 micron or less in diameter, and 0.8 to 0.9 micron indepth. If elements for dynamic random access memory are formed, thedepth may be increased further, for example up to 1 micron or more.Thickness of the stacked layer 520 was about 50 nm at planar potion.Thickness of the tungsten layer 521 was about 0.6 micron. The reason forthem is to bury the contact holes 519 substantially, and to facilitatetungsten polishing by improving planarity of the film surface. Forpolishing tungsten and the stacked layer of titanium nitride or thelike, mixture slurry made from slurry SS-2000 (trade mark of CABOT)containing silica abrasive grain and hydrogen peroxide as oxidizer areused. Polishing conditions other than conditions for slurry were same asabove examples. Tungsten layer 521 may be also polished by usingpolishing apparatus comprising slurry containing substantially noabrasive grain and a carrier according to the present invention, andstacked layer 520 may be then polished and removed by using conventionalslurry containing abrasive grain.

Next, as shown FIG. 12, a first inter-level insulator layer 522 wasformed, and trenches for interconnect was formed, and a first lowermetal layer 523 of 50 nm titanium nitride, then a first upper metallayer 524 of copper film were formed. Thickness of the first inter-levelinsulator film 522 was 0.5 micron. While dry etching technique was usedto form the trenches, the second protection layer 518 of silicon nitrideserved as a stopper against the etching. Since etching rate for siliconnitride is about one-fifth of one for silicon oxide, the thickness was10 nm. Copper of 0.7 micron thickness was formed as the first upperlayer metal layer 524 by electroplating process, and was annealed atabout 350 Celsius degree. The first upper metal layer 524 was polishedby using polishing apparatus with a carrier according to the presentinvention. Another polishing apparatus other than the apparatus used forthe plug polishing, may be utilized if it is needed to prevent coppercontamination in the contact holes. The first lower metal layer 523 waspolished by using mixture slurry which was prepared by adding 0.2 weightpercent BTA to mixture made from slurry SS-W2000 (trade mark of CABOT)and hydrogen peroxide, and by using a second polishing platen (not show)in a second polishing apparatus. The reason for this is to reducepolishing rate of the first upper metal layer. In the process, whenpolishing the first lower metal layer 523, IC1400 (trade mark of RODEL),a stacked structure made of upper layer of polyurethane foam resin andlower layer of flexible resin layer was used as a polishing pad. Thispolishing pad has an advantage that due to soft polishing pad, polishingdamage is not easily generated, providing higher interconnect yieldalthough planarizing effect is decreased comparing to IC1000 pad. Thisis to avoid possibility that if there are complicated structures such asactive device or interconnect in lower level than polished layer,mechanical strength of the interconnect substrate 510 is reducedresulting in easy generation of polishing damage.

A second contamination prevention film 525 of silicon nitride was formedon the surface after polishing by plasma-CVD technique. Thickness of thelayer was 20 nm.

If a variety of active devices are formed on surface of a wafer (aninterconnect substrate) 510 as this example, causing large complicatedsurface height difference, surface of the first inter-level insulatorlayer 522 is not sufficiently planarized so that shallow widedepressions with about 5 nm depth and about same width as devices suchas 5 micron for example, are left, even if the planarization layer 517has been polished. If characteristics of the slurry containingsubstantially no abrasive grain are very good such that it does notgenerate dishing or the like, polishing residue of the first upper metallayer 524 may be then left even in such shallow depressions. In suchcase, the residue of the first upper metal layer 524, if they are, canbe stably eliminated during polishing of the first lower metal layer523, by adjusting BTA concentration added to slurry made from SS-W2000and hydrogen peroxide so that thus prepare slurry has also property topolish the first upper metal layer in certain extent.

Next, a p-TEOS film of 0.7 micron thickness was formed as a secondinter-level insulator film 526, the surface was planarized by 0.2 microndepth by a typical insulator polishing technique with alkali-basedslurry. This planarization was intended to eliminate height differencegenerated during polishing process of the first upper metal layer 524 inthe lower level, or the like. A plasma-CVD silicon nitride film of 0.2micron thickness was then formed as a third contamination preventionfilm 527, and a p-TEOS film of 0.7 micron thickness was formed as athird inter-level insulator film 528. First inter-level connection holes529 and second interconnect trench 530 were formed by using typicalphotolithography technique and reactive dry etching, so that surface ofthe first upper metal layer 524 was exposed. In formation of such trenchpattern with two-step structure, the silicon nitride film serves as anetching stopper. Over the two-step structure thus formed, a siliconnitride film of 50 nm thickness was formed as a second lower metal layer531 by plasma-CVD. A copper film of 1.2 micron thickness was formed as asecond upper metal layer 532 by electroplating method, as shown in FIG.13, and then annealed at 350 Celsius degree.

Next, the second upper metal layer 532 was polished for 5 minute(equivalent to 20% over polishing) for planarization by combination ofpolishing apparatus with the carrier of the present invention and slurrycontaining substantially no abrasive grain, and the second lower metallayer 531 was polished on a second polishing platen (not shown) atpolishing rate of about 200 nm/min with aforementioned BTA-added slurrymade from SS-W2000 and hydrogen peroxide, so that as shown in FIG. 14,two-level copper interconnect with damascene process and dual damasceneprocess was formed. The polishing condition was same as one of thepolishing applied the first upper and lower metal layers, exceptpolishing time.

As described above, by utilizing insulator polishing process andtwo-step polishing process for copper and stacked layer, a multilayerinterconnection can be formed with high yield while maintaining goodplanarity in the surfaces of the respective insulator films and metallayers, providing manufacturing of high performance, large scalesemiconductor integrated circuit devices.

While it has been described about manufacturing process of semiconductorintegrated circuit devices and polishing apparatuses used for it, itshould be appreciated that the present invention is not limited suchexamples and can be applied a variety of surface planarizations oversurface of other workpieces having surface with fine height variationthereon.

According to the present invention, when a metal film such as copper ispolished with slurry containing substantially no abrasive grain, stablefilm polishing is provided by combining use of a polishing apparatuswith fluid pressing mechanism that provides good polishing uniformity,and use of the slurry containing substantially no abrasive grain.Polishing apparatus with fluid pressing mechanism are suitable foruniform polishing over a wafer surface. In order to improve uniformity,support mechanism wherein a wafer is pressed onto a polishing padsoftly, is used. Therefore, a wafer is eccentric with respect to thecenter of a carrier, or twists, during polishing. When slurry containingsubstantially no abrasive grain is used, since the friction is lowerthan friction for conventional slurry with abrasive grain, wafervibration due to unstable eccentricity is easily generated, causingunstable polishing. The present invention essentially reduces thevibration, providing uniform polishing with low damage.

Additionally, since single polishing apparatus according to the presentinvention can be used regardless of amount of abrasive grain containedin slurry, operation and maintenance of apparatus itself are easy.

What is claimed is:
 1. A polishing apparatus, comprising a cover bodywhich is opened at a bottom thereof, has a space therein, and has anelastic membrane indirectly secured to or in a portion of an inner wallthereof through a flexor and a support plate, a surface of the innerwall in a portion at which the secured elastic membrane may contact dueto flex of the membrane or the flexor being made of fluororesin, whereinthe cover body covers a side and a backside surface of a workpieceplaced on a polishing pad on a polishing platen, a surface of theworkpiece is polished by providing relative motion between the polishingplaten and the workpiece while fluid introduced into an upper spaceabove the elastic membrane expands the elastic membrane to press thebackside of the workpiece in a direction toward the polishing platen. 2.The polishing apparatus according to claim 1, wherein a plurality oflateral or longitudinal grooves are provided into the surface of theinner wall comprising fluororesin, and wherein the workpiece is polishedwith the elastic membrane contacting with the surface of the inner wall.3. The polishing apparatus according to claim 1, wherein saidfluororesin is selected from the group consisting oftetrafluoroethylene, trifluoroethylene and fluorovinylidene.
 4. Thepolishing apparatus according to claim 1, wherein the cover bodycomprises a retainer covering the side surface of the workpiece.
 5. Thepolishing apparatus according to claim 4, wherein the retainer comprisesa body portion and a ring of fluororesin embedded in the inner wall ofthe body portion.
 6. The polishing apparatus according to claim 5,wherein said fluororesin is selected from the group consisting oftetrafluoroethylene, trifluoroethylene and fluorovinylidene.
 7. Thepolishing apparatus according to claim 6, wherein the body portion ismade of epoxide resin.
 8. The polishing apparatus according to claim 5,wherein the body portion is made of epoxide resin.
 9. A polishingapparatus, comprising a rotational polishing platen and a rotationalcover body arranged such that it opposes a main surface of the polishingplaten through a workpiece, wherein a bottom of the cover body isopened, the cover body has space therein, an elastic membrane is securedindirectly to or in a portion of an inner wall of the cover body througha flexor and a support plate, the cover body has an introducing inletthat introduces fluid into space above the elastic membrane, and asurface of the inner wall in a portion at which the elastic membrane maycontact due to flex of the membrane or the flexor comprises fluororesin.10. The polishing apparatus according to claim 9, wherein saidfluororesin is selected from the group consisting oftetrafluoroethylene, trifluoroethylene and flurovinylidene.
 11. Thepolishing apparatus according to claim 9, wherein the cover bodycomprises a retainer covering the side surface of the workpiece.
 12. Thepolishing apparatus according to claim 11, wherein the retainercomprises a body portion and a ring of fluororesin embedded in the innerwall of the body portion.
 13. The polishing apparatus according to claim12, wherein said fluororesin is selected from the group consisting oftetrafluoroethylene, trifluoroethylene and fluorovinylidene.
 14. Thepolishing apparatus according to claim 13, wherein the body portion ismade of epoxide resin.
 15. The polishing apparatus according to claim12, wherein the body portion is made of epoxide resin.